1. Field of the Invention
The present invention generally relates to an apparatus for use in a semiconductor fabricating process. More specifically, the present invention relates to a wafer holder and a wafer conveyor system equipped with the wafer holder.
2. Description of Related Art
In a conventional semiconductor fabricating process, an integrated circuit device is fabricated by forming a pattern on a semiconductor wafer, and monitoring the pattern-formed wafer. From a preparation area, a wafer is transferred to an operating area for fabrication and testing. The wafer is placed on an apparatus with its pattern-formed front side or back side facing up depending on the configuration of the fabricating apparatus or the test apparatus. When the wafer's front side is facing down, edges of the wafer is supported by a wafer holder.
As shown in FIG. 1 and FIG. 2, a wafer 18 disposed on a wafer holder (not shown) and in a preparation area of a chamber 10 is safely transferred to an operation area 18′. A wafer-input opening 14 adapted to load wafer 18 into chamber 10 is formed over the preparation area; a test apparatus 12 adapted to monitor the surface of wafer 18 is installed under the operation area.
FIG. 2 shows a conventional wafer conveyor system having a pair of parallel guide rails 20 adapted to linearly move a wafer holder. A thread 20a is formed on a surface of the respective guide rails 20. A wafer holder 25 is disposed between guide rails 20. A base plate 24 of wafer holder 25 has sawtooth-shaped protrusions 24a located where base plate 24 and guide rail 20 come in contact. As guide rails 20 rotate, the sawtooth-shaped protrusions 24a move in conjunction with thread 20a. Thus, wafer holder 25 transfers back and forth between the preparation area and the operation area.
Disposed about its center, base plate 24 has a hollow section 40. A rotatable supporter ring 26 is provided in hollow section 40. In the conventional art, a cylindrical roller 30 and a shaft 22 function as a rotating means. Cylindrical roller 30 is horizontally disposed on base plate 24 along the outer perimeter of supporter ring 26. Shaft 22 is connected along a pivot to rotate roller 30. Roller 30 is also threaded.
FIG. 3 illustrates in some additional detail the conventional wafer holder 25. Wafer holder 25 includes supporter ring 26 and a wafer guide ring 28. Supporter ring 26 is disposed in hollow section 40, and wafer guide ring 28 is disposed inside supporter ring 26. A portion of supporter ring 26 is buried in base plate 24, but sawtooth-shaped protrusions 26a protrude from base plate 24. Sawtooth-shaped protrusions 26a engage the thread of roller 30. When roller 30 rotates by the driving action of shaft 22, the thread of roller 30 engages the sawtooth-shaped protrusions 26a to rotate supporter ring 26. A liner 34 is formed along the inner wall of wafer guide ring 28. The outer edge of wafer 18 is supported by liner 34. The pattern-formed side of wafer 18 faces down on liner 34.
In the conventional wafer conveyor system, when guide rail 20 rotates, sawtooth-shaped protrusions 24a move along thread 20a. Since the movement of wafer holder 25 is perpendicular to the rotational direction of guide rail 20, friction between the sawtooth-shaped protrusions 24a and thread 20a causes the respective parts to wear out. If a part is worn out, time is lost in production when the worn out part is maintained or replaced. Furthermore, frictional wear in a system operating within a clean room environment may further cause particle contamination. If metallic particles become attached to a wafer surface, an integrated circuit device formed on the wafer may become defective, or the entire fabrication process may become contaminated.